Leakage transformer



Jan. 2, 1968 J. F. HARLAND LEAKAGE TRANSFORMER Filed Aug. 5, 1965 INVENTOR z/Zmes fl izarlana ATTORNEY 3,361,934 LEAKAGE TRANSFORMER James F. Harland, Milwaukee, Wis, assignor to McGraw- Edison Company, Milwaukee, Wis., a corporation of Delaware Filed Aug. 5, 1965, Ser. No. 477,531 8 Claims. (Cl. 315-281) ABSTRACT OF THE DllSCLOSURE A transformer having primary and secondary windings, a closed magnetic core linking the windings and consisting of a plurality of laminations and a controlled reluctance shunt path between the windings. The core laminations comprise a plurality of E-shaped members arranged in a predetermined alternating array and abutting L shaped members to form a closed loop. Certain of the I- shaped laminations in the secondary winding yoke section being missing so that its cross sectional area may be selectively increased by inserting laminations.

A method of manufacturing a transformer, including the steps of providing a magnetic core consisting of a plurality of laminations for linking primary and secondary windings, assembling the windings to the core with a predetermined number of laminations in the primary and secondary core portions and providing a controlled reluctance magnetic shunt path between the windings, connecting the secondary winding with a capacitance and gaseous discharge lamp, energizing the primary winding and measuring the lamp power supply, and adding laminations to at least a portion of the secondary winding core section to increase its cross sectional area until the lamp power supply increases to a predetermined value.

Background of the invention This invention relates to a leakage transformer and, more particularly, to a leakage transformer particularly adapted for use as a power supply for gaseous discharge devices.

Gaseous discharge devices such as mercury vapor and fluorescent lamps require a power supply system which provides a high initial voltage sufficient to cause an arc to be struck and which thereafter limits the current flowing through the lamp. In addition, it is often desirable that such power supply circuits maintain the power supplied to the lamp at a substantially constant value regardless of fluctuations in input voltage.

One prior art method of achieving these ends is to provide a leakage transformer in the lamp power supply circuit. Such leakage transformers generally include a primary and secondary winding which are linked by a magnetic core and wherein a controlled reluctance flux leakage path is in shunt between the primary and secondary portions of the transformer core. During the initial starting operation, a relatively high voltage is induced in the secondary winding as a result of the turns ratio of the transformer. Once an arc is struck in the lamp being energized so that current begins flowing in the secondary transformer winding, the secondary voltage drops to the desired normal operating voltage which is substantially less than the lamp starting voltage supplied when the secondary winding is open circuited.

In some prior art gaseous discharge lamp energizing circuits designed to maintain lamp power substantiall constant when input voltage fluctuates a capacitor is connected in circuit between the leakage transformer secondary winding and the lamp so that leading current flows in the secondary winding. This causes an increase 'in the secondary voltage of the transformer which in turn v United States Patent Ofifice 3,361,934 Patented Jan. 2, 1968 may cause saturation of the transformer core in the region of the secondary winding. If this saturation occurs, the transformer secondary voltage is maintained at a relatively stable value regardless of fluctuation of the voltage supplied to the primary winding. Devices operating in this manner are known as Wattage regulating ballasts.

As noted previously, the cores of leakage transformers used in wattage regulating ballasts are provided with a controlled reluctance shunt path between the primary and secondary portions of the transformer core. Prior to the ignition of the lamp, very little leakage flux flows through the shunt path. During this initial starting operation, a relatively high voltage suflicient to strike the arc in the lamp is induced in the secondary winding. However, when current begins flowing in the secondary capacitor lamp circuit and the secondary portion of the transformer core becomes saturated, leakage flux begins traversing the shunt path between the primary and secondary portions of the core. Variations in the flux in the primary portion of the core resulting from variations in input voltage appear as changes in the flux traversing the leakage shunt path and do not appreciably affect the flux in the secondary portion of the transformer core.

It will be appreciated that the capacitor connected in series with the lamp being energized is an impedance which will affect the magnitude of the lamp current. As a result it is desirable to match the capacitor with the leakage transformer so that the desired lamp current will be achieved. However, it has been found that ballast capacitors of the type used in such lamp energizing circuits, are manufactured to a typical tolerance of plus or minus 6 percent. As a consequence, it is necessary to match the transformer and capacitor in each lamp energizing circuit. One prior art method of achieving this result is to stock a large number of capacitors and attempt to match them with the transformer by trial and error. This method is relatively cumbersome and does not lend itself well to high production techniques.

Another prior art method of transformer and capacitor matching is to wind the transformer with a sufficient number of taps such that a suitable one can be chosen to match the capacitor available, but this substantially increases the cost and encumbers the transformer coil winding operation. Yet another prior art method is to place a tap in the transformer after it had been wound by picking the particular secondary coil turn which would give the desired capacitor matching results. This latter method is also not fully satisfactory because of the inherent possibility that adjacent turns of the secondary coil will be damaged.

Another requirement of gaseous discharge lamp energizing circuits is that they provide an alternating current wave whose ratio of peak value to RMS value, commonly called crest factor is less than a predetermined value, usually two. Higher crest factors shorten lamp life by boiling away inordinate amounts of lamp electrode material which then deposits on the lamp arc chamber to also lower light output.

It is an object of the invention to provide a new and improved leakage type transformer for the energizing circuit of gaseous discharge.

Another object of the invention is to provide means for adjusting the secondary current of a leakage type transformer employed for gaseous discharge lamp energizing circuits.

A further object of the invention is to provide a new and improved method of matching a leakage type trans former with the ballast capacitor of a gaseous discharge lamp energizing circuit.

Yet another object of the invention is to provide a leakage type transformer for gaseous discharge energizing circuits and having an improved crest factor.

3 Brief description of the drawings FIG. 1 schematically illustrates the leakage type transformer according to the invention;

FIG. 2 is a schematic view, partly in section, of the leakage type transformer shown in FIG. 1; and

FIG. 3 schematically illustrates the transformer according to the instant invention in a lamp energizing circuit.

Summary of the invention According to one of its aspects the invention comprises the method of manufacturing a transformer including the steps of providing a core for linking a primary and a secondary winding and having a controlled reluctance shunt path therebetween, connecting the secondary winding in series with a gaseous discharge lamp and a capacitance and connecting the primary winding in circuit with an alternating current source, measuring the electrical conditions in the lamp, and adding magnetic material to at least a portion of the secondary winding section of the core to increase the area thereof until the electrical condition in the lamp achieves a predetermined state.

According to another one of its aspects the invention comprises a transformer having a closed magnetic core for linking a primary and a secondary winding and including a controlled reluctance shunt path between the primary and secondary winding sections of the core, wherein the cross sectional area of at least a portion of the secondary winding section of the core has a predetermined cross sectional area which is less than that of the remainder of the core portions, the portion being constructed and arranged for receiving additional magnetic material so that the cross sectional area thereof can be increased from the predetermined value to a second value which is also less than that of the remainder of the core portion.

Description of the preferred embodiment Referring now to the drawings in greater detail FIGS. 1 and 2 show the leakage transformer according to the instant invention to include a core 11, a primary winding 12 and a secondary winding 13. The core 11 comprises a central leg 14 having the primary winding 12 and the secondary winding 13 wound on the opposite ends thereof. The core 11 also includes two side legs 16 and 17 and a pair of yoke sections 18 and 19 which combine to form a return path for the flux in the center leg 14.

The core 11 is composed of a plurality of generally E-shaped laminations 22 and abutting I-shaped laminations 23. As seen in FIGS. 2 and 3 the E-shaped laminations 22 are arranged in groups with alternating groups facing in opposite directions. This creates a plurality of gaps in each yoke of the core 11 and at the open end of each group of E-shaped laminations 22. The gaps formed in the primary winding side of the core are filled by corresponding groups of I-shaped laminations 23 so that in the primary end yoke of the core the groups of E-shaped and I-shaped laminations abut to form a complete core of essentially uniform cross section as shown in FIGS. 1 and 2. For reasons which will be explained more fully herein below, certain ones of the gaps at the open ends of the oppositely facing groups of E- shaped laminations formed in the secondary end yoke of the core are similarly filled with I-shaped laminations. However, certain others of such gap-s are left unfilled as illustrated in FIGS. 1 and 2.

The core 11 also includes magnetic shunts 24 which are disposed between the primary winding 12 and the secondary winding 13 and each is spaced fro-m the legs 14, 16 and 17 of the core 11 by suitable non-magnetic spacer members 25 to provide the desired controlled reluctance shunt path.

Reference is now made to FIG. 3 which schematically illustrates the transformer 10 according to the instant invention as applied to a gaseous discharge lamp 26. Here a ballast capacitor 27 is shown to be connected in series between the secondary winding 13 and the lamp 26.

Prior to the energization of the circuit illustrated in FIG. 3, no current flows in the lamp 26 so that the secondary winding 13 is open circuited. When the switch 23 is closed to energize the primary winding 12, a sufficiently large voltage appears across the lamp 26 to cause an arc to be struck between its terminals 29 whereupon current begins to flow in the circuit of the secondary winding 13.

Because the capacitor 27 is connected in series between the secondary winding 13 and the lamp 26, leading current will flow in this circuit. This causes the secondary winding portion of the transformer core to become substantially saturated. Also, flux begins to traverse the high reluctance path provided by the shunt members 24. In addition, variations in the flux within the primary side of the core 11 resulting from variations in voltage and current supplied by the alternating source as to the primary winding 12 will appear as primarily variations in the flux traversing the shunt path 24 so that the voltage and current values provided by the secondary winding 13 to the lamp 26 will remain substantially constant.

it will be appreciated that the voltage applied to the lamp 26 will be the difference between the voltage induced across the secondary winding 13 minus the drop across the capacitor 27. Because ballast capacitors 27 are normally manufactured to a tolerance of plus or minus 6 percent, the voltage drop that will appear across any given capacitor is not known until the capacitor is actually tested in the transformer secondary circuit. Should the actual drop across the capacitor vary from its nominal value, the current applied to the lamp 26 will either be higher or lower than the predetermined desired value.

In the transformer 10, according to the instant invention, variations in the actual capacitance of the capacitor 27 from its nominal value may be compensated by varying the cross sectional area of the secondary portion of the core 10. This is accomplished by initially leaving out all of the laminations 23 from the secondary winding side of the core 11 as illustrated by phantom lines in FIG. 1. This provides a transformer having a secondary current which is below that required even when the capacitor 27 is at the high end of its plus or minus 6 percent variation from a nominal value. In all cases therefore, the current provided to the lamp 26 will be below the predetermined desired value. The power consumed by the lamp 26 is then measured with a wattmeter M or the secondary current may be measured by ammeter (not shown). The I-shaped laminations 23 are then sequentially inserted into the gaps formed at the ends of the E- shaped laminations 22 until the lamp wattage or current is raised to the predetermined desired value.

The effect of adding a certain number of I-shaped laminations 23 to the secondary winding side of the core 10 is to increase the cross sectional area of this portion of the core thereby to increase the total flux linked by the secondary winding 13 since this portion of the core is operated in the saturation region. As a result, the addition of these I-shaped laminations to the open ends of the E-shaped laminations 22 at the secondary winding side of the core 10 acts to increase the voltage at the secondary terminals of the transformer and thus the current flowing in the lamp circuit and the number of such laminations added therefore determines the amount that this current is increased.

From the foregoing description it will be appreciated that the current supplied to the lamp 26 may be adjusted to compensate for variations in the capacitor 27. Further it will be appreciated that this adjustment in the output in the secondary winding 13 can be achieved without the addition of a plurality of taps to said secondary winding which would greatly increase the cost of winding this coil. In addition the transformer 10 according to the instant invention eliminates the necessity of attempting to choose complementary transformers and capacitors.

In addition, because only the constricted secondary yoke of the core 11 is operated at extreme saturation, the inductance of the secondary circuit is increased over that value which would occur if the entire secondary portion of the core were at said extreme saturation flux density. This provides the desirable result of decreasing the crest factor of the current Wave supplied to the load.

While the invention has been shown and described with relation to one particular core configuration, those skilled in the art will appreciate that it has application to other types of cores as well. In addition, while only a single embodiment of the invention has been shown and described it is not intended to be limited thereby but only by the scope of the appended claims.

I claim:

1. A transformer having a primary winding and a secondary winding, a closed magnetic core linking each of said windings, said core having a primary core section adjacent said primary winding and a secondary core section adjacent said secondary winding, said core including a high reluctance shunt between said sections, at least a portion of the secondary core section of said core having a predetermined cross sectional area which is less than that of the remainder of said main core sections, and means for mechanically selectively increasing the cross sectional area of said section from said predetermined area to a second larger area which is less than that of the remainder of said core sections.

2. A transformer having a closed magnetic core including first and second legs, a primary winding and a secondary winding mounted on said first leg, said core also including a first yoke section adjacent said primary winding and a second yoke section adjacent said secondary winding, a controlled reluctance shunt path provided between said windings, the cross sectional area of the second yoke section being a predetermined value which is less than that of said legs or said first yoke section, and means for mechanically selectively increasing the cross sectional area of said second yoke section from said predetermined value to a second larger value which is also less than that of said other legs.

3. A transformer having a primary winding and a secondary winding, a magnetic core linking both of said windings, a controlled reluctance shunt path provided in said core between said windings, said core including a first plurality of laminations, at least a portion of said laminations having a gap formed therein and adjacent said secondary winding, a second plurality of laminations disposed in abutment with certain ones of the gaps formed in said first plurality of laminations to form a closed loop with said first laminations, at least a portion of the gaps in said core remaining unclosed so that a portion of said core adjacent said secondary winding has a predetermined smaller cross sectional area than that of the remainder of said core.

4. In an alternating current supply system, the combination of, an alternating current source, a gaseous discharge tube having a high initial breakdown voltage and a negative impedance characteristic, a transformer having a primary winding connected to said alternating current source and a secondary winding connected to said gaseous discharge tube, a magnetic core linking each of said windings, a controlled reluctance shunt path provided in said core between said windings, said core including a first plurality of laminations each having a gap formed therein, at least a portion of said gaps being disposed adjacent said secondary winding, a second plurality of laminations being disposed in abutment with certain ones of the gaps formed in said first plurality of laminations to form a closed loop with said first laminations, said second plurality of laminations being less than the number of gaps adjacent said secondary winding, whereby at least a portion of those gaps in said core disposed adjacent said secondary winding remain unclosed so that a portion of said core adjacent said secondary winding has a predetermined smaller cross sectional area than that of the remainder of said core, and a third plurality of laminations insertable in certain of those gaps adjacent said secondary winding so that the cross-sectional area of said core portion may be mechanically increased, and a capacitance connected in series between said secondary winding and said gaseous discharge tube.

5. A transformer having a primary winding and a secondary winding, a closed magnetic core linking each of said windings and a controlled reluctance shunt path provided in said core around said secondary winding, said core including a first plurality of open-ended laminations of magnetic material, at least a portion of said open ends being disposed adjacent said secondary winding, a second plurality of laminations disposed in abutment with the open ends of said first plurality of laminations to form a closed loop with said first laminations, at least a portion of those openings in said core adjacent said secondary winding remaining unclosed so that the cross sectional area of said core adjacent said secondary Winding is less than that of the remainder of said core, and a third plurality of laminations for closing a selected percentage of said openings.

6. A transformer having a closed magnetic core including a first leg, a primary winding and a secondary winding mounted on said first leg, said core also including second and third legs adjacent the remote ends of said primary and secondary windings, respectively, and a fourth leg joining said second and third legs, a controlled reluctance shunt path extending between said first and fourth legs and disposed between the adjacent ends of said windings, said core consisting of a first and a second plurality of laminations of magnetic material, said first plurality of laminations forming said first, second and fourth legs, said second plurality of laminations comprising said third leg and closing the opening between said first and fourth legs, the number of laminations in said third leg being a predetermined quantity less than that in said first, second and fourth legs, whereby said fourth leg has a predetermined smaller cross sectional area than said other legs.

7. A transformer having a closed magnetic core including a plurality of groups of generally E-shaped laminations arranged with adjacent groups facing in 0pposite directions to provide a central core leg and a pair of side legs and a pair of yokes having a plurality of gaps at the open sides of said laminations and alternately at the opposite ends of said core, a primary winding and a secondary winding disposed on the central core leg, a controlled reluctance shunt path extending between said side legs and said central core leg and disposed between the adjacent ends of said primary and secondary windings, said core also including a first plurality of generally I- shaped laminations disposed in abutment with the open ends of the E-shaped laminations facing the primary winding to close the gaps in said core at the primary winding end leg thereof, a second plurality of generally selectively insertable I-shaped laminations disposed in abutment with a portion of the E-shaped laminations facing said secondary winding, the number of laminations in second plurality of I-shaped laminations being a predetermined quantity less than the number of E-shaped laminations facing said secondary winding whereby the core and leg adjacent said secondary winding has a pre determined smaller cross sectional area than said other core legs.

8. A transformer having a closed magnetic core including a first plurality of laminations having first and second legs and an interconnecting yoke section, said first plurality of laminations being arranged so that pre determined adjacent ones are faced in opposite directions to provide a first and a second leg and a pair of yokes 7 having a plurality of gaps at the open sides of said laminations, a primary winding and a secondary winding disposed on one of the legs of said core, a controlled reluctance shunt gap extending between said legs and disposed between the adjacent ends of said primary and secondary windings, said core also including a second plurality of generally I-shaped laminations disposed in abutment with the open ends of the first plurality of laminations facing the primary winding to close the gaps in said core at the primary winding end thereof, a third plurality of generally I-shaped laminations disposed in abutment with a portion of the first plurality of laminations facing said secondary winding, the number of laminations in said secondary winding plurality of I-shaped laminations said first group of laminations facing said secondary winding, whereby the core yoke adjacent said secondary winding has a predetermined smaller cross sectional area than said other core legs and said other yoke.

References Cited UNITED STATES PATENTS 1,606,755 11/1926 Field 336-132 2,346,621 4/1944 Sola 315--239 FOREIGN PATENTS 857,361 12/1960 Great Britain.

JOHN w. HUCKERT, Primary Examiner.

being a predetermined quantity less than the number of 15 J. D. CRAIG, Assistant Examiner. 

